Mg/Ca ratios measured on planktic foraminifera species and reconstructed Sea Surface Temperature (SST) from IODP Site 353-U1443

During the late Miocene, global cooling occurred alongside the establishment of near-modern terrestrial and marine ecosystems. Significant (3 to 5 °C) sea surface cooling from 7.5 to 5.5 Ma is recorded by proxies at mid to high latitudes, yet the magnitude of tropical cooling and the role of atmospheric carbon dioxide (pCO2) in driving this trend are debated. Here, we present a new orbital-resolution sea surface temperature (SST) record spanning the late Miocene to earliest Pliocene (9 to 5 Ma) from the eastern equatorial Indian Ocean (International Ocean Discovery Program Site U1443) based on Mg/Ca ratios measured in tests of the planktic foraminifer Trilobatus trilobus. To test if an atmospheric pCO2 decrease may have driven this cooling, we also present new paleoclimate model simulations under three atmospheric pCO2 scenarios (300 ppm, 420 ppm and 560 ppm; in the range suggested by existing pCO2 proxy records).